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Discussion Starter #1
So, my '85 D150, with the 318 5.2L motor dies once it has warmed up. I assumed it was the O2 sensor, so I went looking in the exhaust manifold. No O2 sensor?? There are only three intrusions into the manifold or pipes. The first two are ports for the Air Injection System. The third is on the passenger side, combined with the Air system and is a what I assume is a butterfly valve attached to an armature with a connection to a round ?? which has a vacuum line running into it. The vacuum line runs up to one of two? Coolant Vacuum Switch Cold Closed valves. So, three questions: What's the round thing, because the armature is broken therefore it's not working. Second, why a isn't there an O2 sensor? Finally, why else might the truck die once warm? Any help is greatly appreciated.
 

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Dbl carb. What do you mean by that? Typically, the D150 318 had a small 2 bbl carb. No O2 sensor because it wasn't a feedback carb. The round thing you mentioned sounds like a "vacuum amplifier" which is physically impossible, but that's what they call it. Does it look like this?

http://www.ebay.com/itm/1973-1974-1...Parts_Accessories&hash=item4ad2b255c0&vxp=mtr

If so, it has to do with the EGR operation. You'll be ahead of the game to just block it off and remove all associated hardware. However, if you are somehow required by your state to have it, it actually did work, and there are still some floating around. They were used from early '70's til late 80's.

Shutting down when warm could be many things. Being an '85, I'd suspect the ignition control box and ceramic resistor (on firewall). When they get old, they will work at first, but once they warm up (electrical current), they fail and the engine loses ignition. Second place to look would be issues with the EGR. Third would be a stuck choke. A rich mixture is fine when warming up, but it'll kill the engine once hot.
 

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Discussion Starter #5
I meant 2 bbl. carb. - I replaced the ICU and resistor a month ago. So that narrows it down to the EGR and choke. I'll block off the vacuum amplifier in a bit and try to clean the choke linkages etc. See if it's those things. I'll leave the EGR for last. Thanks
 
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